Longitudinal plunging unit

ABSTRACT

A longitudinal plunging unit for a shaft assembly used for torque transmitting purposes. The unit includes a profiled sleeve ( 11 ) with circumferentially distributed, longitudinally extending first ball grooves ( 12 ), a profiled journal ( 21 ) with circumferentially distributed, longitudinally extending second ball grooves ( 22 ), balls ( 31, 32, 33 ) which are arranged in groups of balls in pairs of first and second ball grooves ( 11, 21 ), and a ball cage ( 41 ) which is positioned between the profiled sleeve ( 11 ) and the profiled journal ( 21 ) and axially fixes the balls in their positions relative to one another, wherein in the region of the ball grooves ( 12, 22 ), the profiled sleeve ( 11 ) and the profiled journal ( 21 ) include the same torsional stiffness, such that, during the introduction of torque, they are subject to the same angles of torsion.

TECHNICAL FIELD

The present invention relates to a longitudinal plunging unit for adriveshaft assembly.

BACKGROUND OF THE INVENTION

The invention relates to a longitudinal plunging unit for a shaftassembly used for torque transmitting purposes. Such plunging unitsinclude a profiled sleeve with circumferentially distributed,longitudinally extending first ball grooves, a profiled journal withcircumferentially distributed, longitudinally extending second ballgrooves, balls which are arranged in groups of balls in pairs of firstand second ball grooves, and a ball cage which is positioned between theprofiled sleeve and the profiled journal and which axially fixes theballs in their positions relative to one another.

From DE 199 52 245 A1, there is known a longitudinal plunging unit ortelescopic shaft of the foregoing type wherein hardness distortions areavoided in that the number of the first ball grooves corresponds to amultiple of the number of the second ball grooves and wherein the excesspart of the first ball grooves remains free of balls.

EP 0 189 011 A proposes a further longitudinal plunging unit of theforegoing type for torque transmitting purposes. Freedom from play inthe direction of rotation is achieved in that at least one ball orroller comprises an excess dimension relative to the grooves andincludes a resilient material that is fitted under pretension.

When, under torque, the profiled sleeve is displaced relative to theprofiled journal, the balls roll in the inner and outer ball grooves ina way which is substantially free of sliding friction. Thus, the ballsand the ball cage with all its balls, cover half the relativedisplacement path between the two elements, and permit the change inlength of the longitudinal plunging unit in a low-friction way. At theends of the displacement path, axial stops for the ball cage or for theballs are provided in the profiled sleeve or on the profiled journal.Under normal operating conditions, the ball cage should, if possible,not reach the axial stops, but, in accordance with the specified design,it should be freely displaceable, thus avoiding any sliding friction ofthe balls in the grooves.

Assemblies of this type are used in torque transmitting shafts, such asdriveshafts. They are used for the purpose of compensating fortolerances of the distance between the connecting parts during assemblyand/or for compensating for changes in the distance between theconnecting parts, such as joints. These assemblies require low-frictionplunging conditions during operation. The basic design of suchlongitudinal plunging units is known. During operation, they are subjectto a problem in that, during the specified transmission of torque, therenecessarily occurs torsion at the inter-engaging portions of theprofiled sleeve and of the profiled journal in the region of the ballgrooves. As a result, within the groups of balls, the balls of the unitspositioned in the longitudinal direction at the ends are subjected tothe highest loads due to the greatest differences in torsion occurringin those regions. In consequence, there can occur such as damagepittings. This damage occurs at the balls at the ends first, and is thestarting point of the failure of the entire unit.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a longitudinalplunging unit of the foregoing type which has improved running behaviorand, thus, a longer service life.

According to a first solution, in the region of the ball grooves, theprofiled sleeve and the profiled journal comprise the same torsionalstiffness, such that during the introduction of torque, they are subjectto the same angles of torsion. In particular, in the region of the ballgrooves, the profiled sleeve and the profiled journal comprise the samemodulus of transverse elasticity (modulus of rigidity) of the material.They can be made of identical materials, while at the same time they canhave the same polar inertia moment. This solution constitutes a firstmeasure of reducing, under torque conditions, the torsional differences(angular errors) which, if viewed from the center, increase in thelongitudinal direction between the torsion of the profiled sleeve andthus of the outer ball grooves, and the torsion of the profiled journaland thus of the inner ball grooves, in order to ensure that the loads towhich the balls are subjected under torque are as uniform as possible.

A second solution is provided wherein, within the groups of balls, thesize of the balls varies in the longitudinal direction. The ballspositioned centrally in the longitudinal direction have the greatestdiameter and the balls positioned at the ends have the smallestdiameter. In particular, the size of the balls decreases linearly fromball to ball from the center outwardly. However, it is also contemplatedto provide a sub-group of central balls which are identical in size andwhich are adjoined on both sides by smaller balls. The size of the ballsis preferably such that in the torque-free condition of the longitudinalplunging unit, only the central balls are radially pretensioned betweenthe profiled sleeve and the profiled journal. With this solution, it isassumed that, when under the influence of a torsional load, the profiledsleeve and the profiled journal are subjected to increasing torsionstarting from their respective free ends. In such a case, theintroduction of torque via the balls has not yet much of an effect tothe respective connected ends, so that the torsional differences(angular errors) between the two parts are greatest at the respectiveconnected ends which introduce the torque. To ensure that the balls aresubjected to a uniform load, in accordance with the invention, the ballsize is reduced from the center to the respective ends. Best uniformcontact, i.e. uniform ball forces at all balls, should be provided atthe torque occurring most frequently in the load spectrum.

The solutions detailed herein are based on theoretical equations whichact as models for tortional behavior of the plunging unit. To thatextent, it is particularly advantageous to combine the two solutions.

Two preferred embodiments of the invention are illustrated in thedrawings and will be described below. Other advantages and features ofthe invention will become apparent upon reading the following detaileddescription and appended claims, and upon reference to the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of this invention, reference shouldnow be made to the embodiments illustrated in greater detail in theaccompanying drawings and described below by way of examples of theinvention.

In the drawings:

FIG. 1 is a longitudinal section through a longitudinal plunging unitfor the transmission of torque according to a first embodiment of thepresent invention.

FIG. 2 is a longitudinal section through a longitudinal plunging unitaccording to a second embodiment combined with a constant velocityjoint.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a plunging unit with a profiled sleeve 11 having a constantcross-section which is axially followed by a first conical region 13, afirst tubular region 14, a second conical region 15, a second tubularregion 16, a third conical region 17 and a toothed sleeve 18. Into theprofiled sleeve 11 there is inserted a profiled journal 21 with aconstant cross-section which is formed by a solid journal and which isfollowed by a cylindrical journal 23 and a toothed journal 24. Theprofiled sleeve 11 comprises first outer ball grooves 12. The profiledjournal 21 comprises second inner ball grooves 22 whose circumferentialposition corresponds to that of the outer ball grooves 12. However, thenumber of outer ball grooves 12 can be a multiple of the number of innerball grooves 22. The ball grooves associated with one another carry setsof balls 31, 32, 33 which are held, so that they cannot be lost, by asleeve-shaped ball cage 41 in a constant axial arrangement. More thanone set of central balls 31 may be included. Likewise, more than one setof intermediate balls 32 and outer balls 33 may be included. Into theprofiled sleeve 11, there is inserted a sleeve-shaped stop member 42which engages the profile grooves in a form-fitting and positive way andthus has a sealing effect relative to the tube end towards the rightand, at the same time, forms an axial stop to prevent the profiledjournal 21 from being inserted any further into the profiled sleeve 11.It also forms an axial stop for the ball cage 41. A further axial stopfor the balls to prevent the ball cage 41 from being extracted from theprofiled sleeve 11 is formed by a securing ring 44 inserted into anannular groove 43 in the profiled sleeve.

FIG. 2 shows a plunging unit having a profiled sleeve 11 with a constantcross-section which is axially followed by a conical region 13 and by atubular region 14. Into the profiled sleeve 11 there is inserted aprofiled journal 21 with a constant cross-section which is formed by ahollow journal and which is followed by a toothed journal 24. Theprofiled sleeve 11 comprises first outer ball grooves 12. The profiledjournal 21 comprises second inner ball grooves 22 whose circumferentialposition corresponds to that of the outer ball grooves 12. However, thenumber of outer ball grooves 12 can be a multiple of the number of theinner ball grooves 22. Ball grooves which are associated with oneanother carry sets of balls 31, 32, 33 which are held, so that theycannot be lost, by a sleeve-shaped ball cage 41 in a constant axialarrangement. More than one set of central balls 31 may be included.Likewise, more than one set of intermediate balls 32 and outer balls 33may be included. Into the profiled sleeve there is inserted asleeve-shaped stop member 42 which has a sealing effect relative to thetube end towards the right and, at the same time, forms an axial stop toprevent the profiled journal 21 from being inserted any further into theprofiled sleeve 11. A first axial stop for the ball cage 41 is formed bya securing ring 46 inserted into an annular groove 45 on the profiledjournal 21. A further axial stop for the balls is formed by a securingring 44 inserted into an annular groove 43 in the profiled sleeve. Aconstant velocity joint 51 is positioned on the toothed journal 24 byway of its inner joint part 53. The outer joint part 52 of the constantvelocity joint 51 carries a sleeve 54 which clamps in a rolling boot 61.The other end of the rolling boot 61 is positioned on a sleeve 19 which,in turn, is arranged on the profiled sleeve 11 where it is secured by aclamp band 20. A plug 25 for containing the grease filling of the unitis inserted into the toothed journal 24.

In both of the arrangements shown in FIGS. 1 and 2, according to a firstembodiment of the invention, in the region of the ball grooves 12, 22,the profiled sleeve 11 and the profiled journal 21 comprise the sametorsional stiffness. Thus, they are subjected to the same angles oftorsion when torque is introduced. According to a second embodiment ofthe invention, the central balls 31 have a greater diameter than theintermediate balls 32, and outer balls 33 positioned towards the ends.The ball grooves 12, 22 in both FIGS. 1 and 2 have a constantcross-section. When the longitudinal plunging unit is subjected totorsion, higher forces are applied to the intermediate balls 32 andouter balls 33 only after the profiled sleeve 11 and the profiledjournal 21 begin to be subjected to torsion, so that the expectedaverage torque range all balls 31, 32, 33 are subjected to uniformHertzian pressure relative to one another.

From the foregoing, it can be seen that there has been brought to theart a new and improved longitudinal plunging unit. While the inventionhas been described in connection with one or more embodiments, it shouldbe understood that the invention is not limited to those embodiments.Thus, the invention covers all alternatives, modifications, andequivalents as may be included in the spirit and scope of the appendedclaims.

1. A longitudinal plunging unit for a shaft assembly used for torquetransmitting purposes, comprising: a profiled sleeve withcircumferentially distributed, longitudinally extending first ballgrooves; a profiled journal with circumferentially distributed,longitudinally extending second ball grooves; balls which are arrangedin groups of balls in pairs of first and second ball grooves; and a ballcage which is positioned between the profiled sleeve and the profiledjournal and axially fixes the balls in their positions relative to oneanother, wherein, in the region of the first and second ball grooves,the profiled sleeve and the profiled journal comprise the same torsionalstiffness such that, during the introduction of torque, they are subjectto a same angle of torsion.
 2. A longitudinal plunging unit according toclaim 1 wherein, in the region of the first and second ball grooves, theprofiled sleeve and the profiled journal comprise the same polar inertiamoment, and each comprise a material having the same modulus oftransverse elasticity. 3.-6. (canceled)
 7. A longitudinal plunging unitaccording to claim 1 wherein at an end of the profiled journal whichprojects from the profiled sleeve, there is arranged a constant velocityball joint, and a convoluted or rolling boot is secured to an outer partof the constant velocity joint and to the profiled sleeve. 8.-10.(canceled)
 11. A longitudinal plunging unit according to claim 7wherein, in the region of the first and second ball grooves, theprofiled sleeve and the profiled journal comprise the same torsionalstiffness, such that, during the introduction of torque, they aresubject to a same angle of torsion. 12.-14. (canceled)
 15. Alongitudinal plunging unit for a shaft assembly used for torquetransmitting purposes, comprising: a profiled sleeve withcircumferentially distributed, longitudinally extending first ballgrooves; a profiled journal with circumferentially distributed,longitudinally extending second ball grooves; a sleeve-shaped stopmember in the profiled sleeve and providing an axial stop for theprofiled journal; balls which are arranged in groups of balls in pairsof first and second ball grooves; and a ball cage which is positionedbetween the profiled sleeve and the profiled journal and axially fixesthe balls in their positions relative to one another, wherein, in theregion of the first and second ball grooves, the profiled sleeve and theprofiled journal comprise the same torsional stiffness such that, duringthe introduction of torque, they are subject to a same angle of torsion.16. A longitudinal plunging unit according to claim 15, wherein at anend of the profiled journal which projects from the profiled sleeve,there is arranged a constant velocity ball joint, and a convoluted orrolling boot is secured to an outer part of the constant velocity jointand to the profiled sleeve.